title: Reduced dopamine output in the nucleus accumbens but not in the medial prefrontal cortex in rats displaying a mecamylamine-precipitated nicotine withdrawal syndrome.
abstract: Mesolimbocortical dopamine (DA) neurotransmission is important in the mediation of the dependence-producing actions of nicotine and other drugs of abuse. Withdrawal from chronic treatment with various types of addictive drugs, including amphetamine, cocaine, ethanol and morphine is associated with a decrease in dopaminergic output in the nucleus accumbens (NAC), whereas the effects of withdrawal from these drugs on dopaminergic output in the medial prefrontal cortex (PFC), as yet, remain largely unknown. This study examined putative changes in the extracellular levels of dopamine and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the NAC and in the PFC of rats displaying behavioral signs of nicotine withdrawal. Rats were infused for 7 days with nicotine via subcutaneously implanted minipumps, whereas control animals carried saline-containing pumps. On the fifth day of infusion a microdialysis probe was implanted in the NAC or the PFC of the rats. Forty-eight hours later the levels of DA and the monoamine metabolites were assessed in the dialysate. The behavioral and biochemical effects of a saline injection and a subsequent challenge with the nicotinic receptor antagonist mecamylamine (1 mg/kg s.c.) were determined. Following mecamylamine challenge in nicotine-treated animals, the levels of DA, DOPAC and HVA in the NAC, but not in the PFC, decreased below pre-injection levels and in relation to control animals. The score of abstinence signs increased in the nicotine-treated rats, as compared both to the score after saline and to that in control animals. The decreased DA output in the NAC in animals displaying nicotine withdrawal signs is similar to that seen after withdrawal of several other drugs of abuse, and may have bearing on motivational deficits associated with the abstinence reactions.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: B E
authors.initials: BE
authors.lastname: Hildebrand
authors.forename: G G
authors.initials: GG
authors.lastname: Nomikos
authors.forename: P
authors.initials: P
authors.lastname: Hertel
authors.forename: B
authors.initials: B
authors.lastname: Schilström
authors.forename: T H
authors.initials: TH
authors.lastname: Svensson
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004298:Dopamine / Q000378:metabolism*; D006719:Homovanillic Acid / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D009538:Nicotine / Q000009:adverse effects*; D018733:Nicotinic Antagonists / Q000494:pharmacology*; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013375:Substance Withdrawal Syndrome / Q000209:etiology*
chemical_list: D018733:Nicotinic Antagonists; D015102:3,4-Dihydroxyphenylacetic Acid; D006897:Hydroxyindoleacetic Acid; D008464:Mecamylamine; D009538:Nicotine; D004298:Dopamine; D006719:Homovanillic Acid